Ultraviolet radiation is an important workhorse in the industrial community for promoting chemical reactions, initiating chemical reactions, degrading organic and non-organic molecules, inducing mutations in biological systems, acting as an antiviral and bactericidal agent and the like. Normally the source of the ultraviolet radiation is emitted from an electric discharge lamp having various types of gases which when excited by the electric discharge, emit UV radiation. These lamps are generally categorized as low or medium/high intensity lamps. They may operate at low or high pressures for gases within the lamps. Normally the lamps are of a quartz material which is transparent to the emitted UV radiation. The lamps may operate at low or high temperatures ranging from approximately 30.degree. C. up to 950.degree. C. The output of these lamps may range from less that 40 watts to in excess of 30,000 watts. The lamps may be even customized to the extent that a certain portion of the UV spectrum is omitted or enhanced rather than the entire portion of the UV spectrum.
A driving force for such variety in UV lamps is that each of the above industrial applications requires lamps having different UV intensities, different wavelength of emission, operating pressure and temperatures and power requirements.
Normally the lamps, as employed in reactor systems, particularly reactor systems which have fluids passing therethrough, such as aqueous media, have a variety of UV transparent protective sheaths within which the lamps are placed so that the lamps do not come in contact with the material being treated by the UV radiation. This technique protects the quartz of the UV lamp and the electrical connections to the lamp electrodes. Also it can facilitate lamp replacement without having to disassemble down the reactor.
One of the significant problems with UV transparent protective sheaths for the UV lamps is the fact that materials within the fluid being treated may deposit on the sheath exterior surface and hence reduce the degree of UV radiation transmitted through the sheath thereby reducing the effectiveness of the reaction or UV treatment taking place within the reactor.
A variety of approaches have been provided to overcome this significant problem in reduction of the UV transmission through the protective sheaths during reactor operation. The most common approach has been to shut down the reactor after several hours or days of operation to permit removal, cleaning and replacement of the protective sheaths. This is an expensive time consuming procedure for lamp cleaning. The problem however with other cleaning devices is providing systems which are resistant to high intensity UV radiation and when necessary can withstand close proximity to the very high temperatures of the high pressure high intensity lamps which may reach 950.degree. C.
Examples of cleaning systems used with low temperature UV lamps are disclosed in U.S. Pat. Nos. 3,462,597; 3,562,520 and 3,904,363.
U.S. Pat. No. 3,462,597 discloses a UV lamp system for use in water purification by virtue of the bactericidal and other UV sensitive contaminants being neutralized in the water. The system involves the use of a lamp which operates at a temperature of approximately 105.degree. F. i.e. in the 30.degree.-35.degree. C. range. Since the contaminated water to be treated contains certain physical impurities which tend to deposit on the outside of the quartz tube, such deposits including mineral deposits, protein deposits and the like. A wiper system is provided for the protective sheath for the UV lamp. The wiper system comprises wiper rings which are made of teflon or any other material not affected by UV radiation and are spaced apart from one another. The rings are preferably split and are elastically or resiliently held on the outside of the protective tube by a garter spring. This provides for "efficient" wiping action. The wiping rings are on a ring holder and a rod which extends through an end or the reactor engages the ring holder. The ring holder is then reciprocated to provide a wiping action along the protective tube to remove physical or biological materials which had deposited on the outside of the protective tube. This system is totally inadequate however by virtue of the dimensional variations in the protective tube which is normally made of quartz and the inability to resist high temperature operations in the range of 350.degree. C. to 800.degree. C. The teflon would immediately deteriorate at such high temperatures. The elastic garter is normally inadequate to vary the dimension of the wiping rings during use as the rings are moved along the quartz tube.
U.S. Pat. No. 3,562,520 discloses another type of water purifying apparatus involving the use of a wiper system to routinely clean the protective tube made of quartz for the UV lamp position within the reactor. The wiper system consists of a number or ring-like wiper elements surrounding and in wiping contact with the external surface of the protective tube. The wiper assembly is urged along the tube by a coil spring. When water to be treated flows through the reactor the wiper returns to the other end of the tube to effect a wiping of the area of the tube between the inlet and outlet of the treatment system. This ensures that the protective tube is clean of deposits during each start-up of the water purifying device, however, should water flow through the device for any extended period of time, deposits from the water may reform on the protective tube thereby reducing the degree of UV transmittance and thereby the effectiveness of the radiation in treating bacteria in the water. This system would be totally inadequate for treatments involving continuous flow of water over extended periods of time.
In U.S. Pat. No. 3,904,363 a similar problem arises as with the device of U.S. Pat. No. 3,562,520. The wiper system is activated by water flow. For an extended continuous flow of water, the protective tube would not be cleaned. The flow of water moves the wiper system to one end of the tube and keep it there. When the water shuts off, due to the vertical orientation of the reactor, the wipers descend to the base of the reactor under the influence of gravity. The wiper system is made up of a flexible semi-rigid plastic or flexible metal membrane. The membrane may be a brush-like textured membrane of composite or plastic material. The membrane however in contacting the protective tube, is very thin and is usually inadequate for removing stubborn deposits on the protective sheath. Furthermore, under high intensity UV radiation from high powered lamps, the plastic version of this wiper would deteriorate rapidly.
It has already been mentioned that UV radiation is used in a variety of commercial applications. Applications where deposits on protective sheaths for the UV lamps are particularly troublesome is in the treatment of waste aqueous media related to ground water pollution, organic chemical manufacturing, petroleum refineries, wood preserving operations, pulp and paper bleach plant effluent, multicontaminant landfill leachates, electroplating in metals treatment, explosives manufacturing, handling low level toxins in drinking water, air streams contaminated with volatile organic components, contaminated non-aqueous liquids and solvents and chlorinated organic solvents. A reliable low maintenance system for removing deposits on the protective tubes is desired to ensure efficient operation of the reactor over extended periods of time.